1. Field of the Invention
The present invention relates to an inkjet printer, particularly to a line type inkjet printer wherein a plurality of nozzles are arranged over the length corresponding to the width of a printing medium and ink is emitted from these nozzles to the aforementioned printing medium, whereby an image is printed.
2. Description of the Related Art
In some of the inkjet printers according to the conventional art, fine ink particles are emitted to a printing medium from the nozzle of an inkjet head in response to the emission control of an image signal, and at the same time, the inkjet head is moved in the main scanning direction to perform image printing for one line. Then the printing medium is shifted by one line in the sub-scanning direction and fine ink particles are again emitted from the inkjet head nozzle to the printing medium to perform image printing for one line. This procedure is repeated, thereby forming an image on the printing medium.
In another inkjet printer according to the conventional art, the inkjet head is designed in a longer type wherein the ink emitting nozzles are arranged at an equally spaced pitch over approximately the maximum printing width of a printing medium, so that the inkjet head constitutes a line head secured on the apparatus proper. This structure eliminates the need of the inkjet head moving in the main scanning direction, and permits an image to be formed merely by conveying the printing medium in the sub-scanning direction, the printing medium being perpendicular to the main scanning direction. This arrangement ensures high-speed image formation.
However, because of high-speed image formation, the printing resolution in the main scanning direction is determined by the nozzle pitch of the line head when an image is formed by only one step of conveyance in the sub-scanning direction. Thus, to provide a finer pitch of printing dots in the main scanning direction, the line head nozzles could be arranged at still finer pitches, thereby getting a finer dot pitch. However, there is a limit to machining when making the nozzle pitch finer. Hence there is a limit to printing precision that could be achieved by a finer dot pitch. This method further involves problem of increased costs.
The following line head is proposed in the Japanese Non-Examined Patent Publication 11-34360. According to this document, to improve the printing precision in the main scanning direction, a plurality of the printing heads having nozzles arranged in a straight line are provided in the sub-scanning direction. Each printing head is sequentially displaced in the main scanning direction by a fraction of one printing head with a space L between the aforementioned nozzles, whereby a set of inkjet heads is formed. A plurality of sets of inkjet heads are oriented across the width of the paper, and are placed in staggered arrangement over the entire width of paper compactly without leaving any space.
However, in the line head disclosed in the Japanese Non-Examined Patent Publication 11-34360, a plurality of printing heads with the nozzles arranged in a straight line are displaced in the main scanning direction, whereby a set of inkjet heads is formed. Thus, to improve the printing precision, multiple printing heads must be arranged. However, each printing head is a inkjet head having been manufactured independently, and therefore, each printing head must be positioned so as to adjust the positions of nozzle surfaces of all the printing heads. This involves a problem of complicated assembling work to be performed.
Each printing head is an independently completed inkjet head. Assembling of these heads results in a large-sized inkjet head in the final stage.
Furthermore, when the head is replaced, a complicated work procedure is required in reassembling the head by positioning.